All The Things We Never Knew
by daughter of athena 2000
Summary: We always see the strong side of Isabelle Lightwood; after all, most people do. But what happens when Isabelle is away from the crowds? What happens when she gets too drunk one night, or when she has a rough day and needs someone to vent to? A one-shot collection in alphabetical order that shows the special relationship between Izzy and Alec.
1. Chapter 1

AN: Hey guys! So please forgive me because first of all, this is a short one and two, I have not read all of the books and I wasn't able to watch all of the Shadowhunter's episodes before it went off air. I have been catching up, however, so bear with me. As I said, this one is short but not all of them will be. Also, this will mostly be exploring the weaker or sweeter side of Izzy that only Alec really sees, mostly because I love their sibling relationship and I feel like we see enough of tough Izzy as it is. She is my favorite and I am in no way trying to be sexist or anything, I just want to explore an unseen side of her. So with all of that being said, thanks for reading, and I hope you like it!

Disclaimer: I do not own The Mortal Instruments or Shadowhunters.

"The 'A' says, 'ah,' Izzy. 'Ah, ah, ah.'" Alec Lightwood sat with his now two year old sister in the library of the Institute, excited to show his favorite family member what Hodge had taught him that day. Izzy's chubby cheeks smiled widely as she watched the funny way in which her brother said the letters, giggling and earning a bright smile in return from Alec. "Now you try!"

Isabelle's small face contorted, making it seem like she was really focusing. She opened her mouth before shutting it again, seeming almost afraid that her big brother would get mad at her if she messed up. Seeing this, Alec smiled encouragingly and said, "You can do it Iz! I know you can! Just remember, the 'A' says, 'Ah'." Dark brown eyes met bright blue as Izzy's mouth started to open once more, eventually letting out a little sound akin to the letter "A".

"That was great Iz! Try again!" This time she got closer, impressing the little boy because he knew his sister was smart for her age, but he wasn't sure she could quite get letters down yet. "Okay, now try 'L.' Remember, the 'L' says, 'luh, luh, luh.'" Again the small girl tried, and after a minute she again proved to be successful.

On and on they went, although really, Alec figured, they only had two more letters to go. Once she had learned "E" and "C", Alec figured she was ready to jump ahead a little bit. "A-L-E-C. Alec. Say it with me Izzy, Alec."

"Awec," Isabelle stated confidently, looking confused when her older brother let out a frustrated sigh.

"No, Iz, my name is ALEC, not Awec!" At his unintentionally loud tone the little girl's eyes filled up with tears, thinking that she had upset her favorite person in the world. Upon seeing his baby sister's tears, Alec's eyes got wide and he quickly took her into his arms, rocking her gently and smoothing back her curly hair. "It's okay Iz, really it is! I'm sorry, I didn't mean to be too loud."

Slowly but surely the little girl calmed, finally looking at her older brother and letting out another loud giggle at the fearing look in his eyes. Alec giggled with her, loving to see his Izzy laugh. Once again they got to work, and although Isabelle never did quite get his name right, Alec figured that it was okay because "Awec" was actually kind of growing on him.

A now twenty-five year old Izzy sat with her older brother on the couch of her home with Simon, watching her two children play. A boy and a girl, her kids were said to be her and Alec incarnate, impeccably like their mother and uncle without even realizing it. Alec put his arm around Isabelle as he watched his nephew explain to his niece what sound the "G" makes. Drawing her closer, Alec placed a kiss on his sister's forehead and she leaned into him a little more, resting her head on his shoulder.

"You know," Alec whispered, not wanting to interrupt the two tots on the ground, "that was how I taught you to say my name when you were about her age."

Izzy lifted her head ever so slightly to look at her brother. "Really?"

"Mhm." Both Lightwood siblings smiled, the same wide, toothy grins that they had smiled together in the library all those years ago.

"So did I get it?"

Alec laughed a little. "No, but you got close. You refused to say anything but 'Awec'."

"Really? That's so cute!"

Alec pretended to look annoyed, but secretly he remembered how much more adorable it made his baby sister to call him that. It really was nothing, if you thought about it; just a silly name that very well could have been anything else. But he was her "Awec" and she was his "Izzy", and those two names had become much more than names: they had become terms of endearment.

"Oh come on, Awec, you know you thought it was cute." Isabelle's teasing voice cut through his thoughts as she lightly pinched his cheek, making him swat her hand away gently.

He scoffed. "Whatever."

A gasp escaped Isabelle's mouth, somehow missed by his niece and nephew. "You DID think it was cute!"

"Izzy, I-"

"Admit it, admit that you thought it was cute!"

He sighed. "I guess, at the time, it-"

Isabelle shot her hands up in the air victoriously. "YES! I win!"

Alec rolled his head back and let it touch the couch, saying, "By the Angel, I never should've told you that story."

Izzy just laughed again, making her older brother smile as she cuddled up to him again. "I love you too, Awec."

AN: So there it is! I know this one is kind of short, and some will be depending on the content. I plan to go in alphabetical order, so please let me know if there is anything you would like to see in future one-shots! Thanks for reading, reviewing, favoriting, and following, if you do! Later! :P


	2. Birthdays

**AN:** Hey guys! I'm SO sorry that this took a long time, I've been incredibly busy. But I'm back now, and I would just like to thank all of you that have read, reviewed, favorited, and followed! It means a lot, and I always love your feedback. Please let me know if there's anything you would like to see, and thanks for reading! I hope you like it!

 **Disclaimer: I do not own The Mortal Instruments or Shadowhunters.**

* * *

"I said no!" Izzy's voice echoed from her bedroom, causing Alec to look up from the book that he was trying to enjoy in his bed. Sighing, Alec bookmarked the page and set it aside, figuring that he should check on his sister even if she was disturbing his very rare moment of peace and quiet. As he walked down the hall, the sound of a frustrated Isabelle flinging things around rang out. No doubt there would be another dent in the wall by the door, and Alec ran a hand over his face at the thought of having to cover for her yet again.

When he stepped in her doorway, the first thing Alec noticed was just how annoyed Isabelle looked, and he grimaced at the thought of what she would be doing to the poor soul who managed to piss her off. Just like he had predicted, there were shoes and dresses flung everywhere, a muttering Izzy in the middle of them. "Iz?" Alec said, causing the girl to look up at him with a red face.

Alec raised an eyebrow at his sister before walking over to her bed and plopping himself down, legs crossed. "Alright, what's wrong?"

Izzy huffed. "It's nothing," she grumbled, looking down at the clothes on the floor.

"Oh yes it is. You love your clothes, you wouldn't be throwing them around for 'nothing'."

Isabelle gave him an annoyed look before relenting. "Fine. It's Simon, he-"

"Did he hurt you Iz?" Alec cut her off, a furrowed brow and deep frown painted on his features. Now Izzy sighed; her brother's over-protective side was coming out again.

"No, he just...he wants to celebrate my birthday."

Now Alec's brows rose, a small smile gracing his face as his sister scowled at him. "That's it? That's what this is about?"

"Yes, 'that's what this is about'," Isabelle sneered, though Alec didn't let it hurt his feelings because he knew that his sister wasn't actually angry at him; she was just angry at her idiot boyfriend. Vaguely Alec considered warning Simon to flee the country, but then decided against it. He didn't really care for Simon, and besides, Izzy could find him no matter where he was.

"Iz, he just wants to celebrate your birthday."

Izzy gave him an exasperated look. "Alec, you and I both know that I don't like to celebrate my birthday."

"I don't see why not."

"You love following the rules more than anyone else I know. This is the one rule I actually want you to follow, so why don't you?"

"It's not against the rules to celebrate Iz."

"Yes it is! We don't associate ourselves with mortal holidays, remember?" Isabelle raised her eyebrows, brown eyes widening as she hoped for her brother to see reason. No such luck.

"It's not a rule, exactly, it's just that a lot of us don't. We can if we want to, remember?" he mocked her, smiling as she grew even more exasperated.

"Alec, I don't like celebrating my birthday! I don't understand why you do!"

With a smile still on his face, Alec got up and walked over to his baby sister, pulling her into his arms and resting his head on her's. "You don't know why I like celebrating your birthday with you?" Izzy shook her head. "Because the day you were born was the day I was blessed with my best friend." Alec felt Izzy smile into his shirt, which caused his smile to grow impossibly more as he planted a kiss on the top of her head. Isabelle pulled back a little bit to look at her brother, staying in his embrace as she smiled up at him. Alec pushed a piece of hair behind her ear before continuing, "Let Simon do something for your birthday. Even if it's something small. He just wants to show you how much he cares for you."

Isabelle contemplated for a moment before replying, "Fine, I guess it can't hurt too badly."

"That's a girl." Alec gave her one last squeeze before pulling away. "Now, clean up your room. It's a total mess."

Izzy put her hands on her hips and cocked her head to the side. "What, can't be bothered to help your little sister?"

"Normally I would, but I have some business to attend to." With that, Alec walked out of her room, leaving Isabelle behind shouting after him and asking what business he could possibly have.

* * *

"Lewis. Hey, Lewis!" Simon turned around, a dorky smile appearing on his face before being replaced with a look of apprehension. Alec sighed (which he seemed to be doing a lot lately, he noted) and ran a hand over his face; this was going to be a long couple of days.

"Uh, hey Alec, what's uh...what's up?" Simon tried to look friendly, but found it rather hard. He knew that Isabelle's brother didn't care for him, but he loved Izzy so he put up with it for her sake.

"Look. I don't like you, you know I don't like you, whatever. But I love Isabelle, and I want to make her birthday special. Now I talked her into letting you plan something for her, but I'm going to help you plan it so you don't screw it up and ruin her special day."

Simon snorted obnoxiously, making Alec want to punch him. "Well that's very nice of you Alec, but I think I can plan my own girlfriend's birthday party. Besides, Izzy is a big girl; she doesn't need her brother running around and sticking his nose into her business."

Alec grabbed the front of Simon's shirt and pushed him up against a nearby wall. Putting his face close to Simon's, Alec growled, "Look, vampire. I don't care about you, quite frankly I would happily run you through with a blade right now. Izzy is my baby sister. I love her, and whether or not she wants to admit it, she is always gonna need Jace and I, even as capable as she is. But you? You are completely dispensable. And you will NOT mess up her birthday, so I will help you and you will deal with it and listen to what I say." Alec finally let Simon down, adding, "And you can wipe that stupid look off your face."

Simon's "tough guy" demeanor had vanished, and now he listened quietly.

"So," Alec said, crossing his arms, "What do you have planned?"

* * *

"Jace, I'm telling you, he's got the worst idea in the history of the world. It's like he doesn't even know Izzy at all!" Alec paced, ranting to his parabatai who sat listening on his bed.

"Alec, it can't be that bad," Jace argued gently, noticing how upset his brother was getting.

"Jace, he wants to give her a bunch of glittery pink balloons."

"Oh no, you're right, he's an idiot."

"Oh yeah."

Jace frowned in concentration before saying, "Okay, he's going to ruin this for her. I mean seriously, glitter? Pink balloons? She's kinda girly sometimes but she's not a total princess. She'll hate that!"

"I know!" Alec sighed. "I'm starting to regret ever talking her into this."

"Wait, you talked her into letting Lewis throw her a party?"

"Yes, because I thoought that it was slightly salvagable! Now, I'm not so sure."

Jace didn't exactly know what to do; normally, he and Alec would just take Izzy shopping or spar with her or let her make dinner for them one night and not throw up in front of her. They seemed to be the only two that she wanted to celebrate anything with, probably because she had terrible trust issues. He couldn't stand Simon, and he really only tolerated him for Clary and Izzy because they were the two most important women in his life. But if Lewis managed to ruin their little sister's birthday, he was going to tell Clary that she'd have to find a new best friend because Simon would be dead.

"Look, all we've gotta do is interfere," Jace reasoned, causing Alec to snort and look over at him.

"Oh, good idea. Now how do you suppose we do that?"

"I...I don't know. But we'll figure it out!" Jace caught Alec's eye, and the two stared at one another as Jace continued, "Look, our main goal is to make sure that Iz has a great birthday. We'll deal with the Simon thing as much as we can, but our focus is going to be our sister."

Alec nodded. "I agree. So, what's the plan?"

* * *

Isabelle was lying in bed, still half asleep as the rays of sunshine poured through her sheer curtains. Groaning, she remembered what day it was and felt a sense of dread rush through her; there was no telling what Simon had planned, and if her brothers had anything to do with it then it would be ten times worse. She really didn't want to celebrate her "big day" at all, but it made her boys happy, so she figured she could handle it for one day.

Suddenly her ears picked up on footsteps thundering down the hall, seemingly coming to her room. Izzy had just picked her head up when her door burst open, a beaming Jace running into her room and jumping on top of her on the bed. "IT'S YOUR BIRTHDAY IT'S YOUR BIRTHDAY IT'S YOUR BIRTHDAY!" he yelled, making Izzy laugh at how much he resembled a little kid. If anyone else had done this, they probably would've had a lovely interaction with her whip and the heel of her boot. But this was Jace, and he was the only person besides Alec who could avoid her wrath...most of the time.

"Jace, get OFF!" Isabelle shouted, shoving him although she was laughing along with him. Jace did get off but started pulling at her hand, attempting to drag her out of bed as gently as possible. "Jace, no!" Izzy groaned.

"Izzy, yes!" Jace mimicked.

Finally his sister relented, getting out of bed slowly as Jace grinned in delight. Once she was up, Jace's smile grew as he took in her messy bed head and old t-shirt and shorts; his little sister always looked so done up, which was fine, but she was naturally beautiful and it was great to see her not care every now and then. Isabelle raised an eyebrow, smiling up at him. "What?" she asked, putting her hands on her hips.

Jace pulled her into a hug, squeezing gently. "Happy birthday, Izzy."

Isabelle squeezed him back. "Thanks Jace."

Jace pulled away but kept his arm around her shoulders. "Come on kiddo-"

"I'm not that much younger than you!"

"-I think Alec's making breakfast."

Izzy glared half-heartedly. "One, I don't appreciate being interrupted, and two, you guys don't have to do that."

"We don't have to, but we wanted to! Besides, one of the perks of being your brothers is that we can dote on you on your birthday and you can't be annoyed at us."

"Oh really?" Isabelle snorted and raised an eyebrow, a small smile on her face.

Sure enough, when they arrived in the kitchen of the Institute Alec was at the stove, cooking what appeared to be pancakes. When he heard them enter he turned, smiling as his little sister walked over to him and hugged his waist. "Thank you for breakfast, Alec," she said quietly. Alec knew that Izzy didn't like to be doted over, and she really didn't like to celebrate her birthday. But her brothers were her weakness, and she was their's; the siblings were an unbreakable trio, and they saw all of the good and the bad within each other. Growing up with only each other and Hodge for company could do that.

"No problem, sis," he whispered back, kissing her on the head. "Happy birthday."

* * *

Isabelle had just finished getting dressed for...whatever it is they were doing. All Simon had told her was to be ready for seven and to dress casually. Of course, that didn't stop her from dressing in her usual fabulous fashion, but it was nice to know that he hadn't gone to the trouble of doing anything fancy. Slipping one more pin into her hair, Izzy sat back, satisfied. Spying a picture of herself, Alec, and Jace, she smiled. It had been a birthday present from Clary earlier in the day, even though Isabelle had told her that she didn't need any presents. Isabelle had only had it for a few short hours, but the image of herself with her brothers on either side of her, smiling widely with their arms around one another, had already become one of her most prized possessions.

A knock on her door broke her out of her thoughts. "Come in!" she called, and Alec's walked in, buttoning the last button on his shirt.

"Hey Iz, can you-wow, Izzy, you look beautiful." Alec's eyes shone with love and a little pride; his baby sister had grown up, and it made him both sad and proud at the same time.

Isabelle broke out into that wide smile of her's before saying, "Me? Look at you! You look so handsome." Walking over to her brother, Izzy helped him straighten out his collar and smooth out the nice black button-down he had chosen.

Alec let her help but grabbed her hands to stop her when she reached for his hair. "Okay mom, let's go." Izzy rolled her eyes and grabbed her whip, letting it snake around her wrist before following her brother out the door.

* * *

It turned out that Simon had actually done an okay job. There were balloons with glitter, but Alec had managed to talk Simon out of pink and replaced them with purple.

He had somehow managed to rent out Taki's for a night, which surprised Jace because as far as he knew Simon was incredibly broke. When he asked him about it (which Clary and Izzy had both smacked his stomach for because apparently it was "rude") Simon just shrugged and said that he may or may not have to play there with his band for the next year, but it was worth it because it was for his "special lady". That part made Jace want to smack him; his "special lady" had a name, and it was Isabelle which in Jace's opinion was a very nice name and should be treated as such. Alec had simply rolled his eyes and given their sister a sideways glance, asking her with his eyes if she was really sure she wanted to date this loser. Izzy rolled her eyes in response and gave Simon a quick hug and kiss on the cheek, thanking him for going out of his way.

As much as they hated to admit it, Jace and Alec both agreed that while it was a little much, it was nice of him to do this for Izzy. That didn't mean they liked him of course; when Simon's bandmates (who were the musical entertainment for the night) had played a slow, sappy song for the couple to dance to, Alec and Jace both looked at each other and gagged. No, they didn't have to like him, but if he made their baby sister happy then that was good enough for them.

Jace looked at his parabatai, who sat across the table from him in a booth. His eyes were trained on Izzy, watching her with a small smile on his face and a little sadness in his eyes. "Hey," Jace murmured, causing Alec to return his gaze, "You okay?"

Alec nodded a little before turning his head to look at Izzy again. She was looking up at Simon as if he was the only other person in the room, drifting along slowly with him as he gave her the exact same attention. "She's so grown up," Alec whispered. "I mean, that happened a long time ago. It's not like she's a baby. But it's like I can't stop seeing that little two year old girl who would cling onto me when she was scared of the thunder. The same one who didn't know whether to stand behind or in front of me when you first arrived and we didn't know what to make of you."

Jace gave him a sympathetic look. "I know what you mean. I mean, I wasn't there when she was born; I don't share your blood-"

"We still think of you as if you do."

Jace shot Alec an appreciative smile. "I know. My point is, I didn't even know Izzy at a time in her life when she needed protection. Since the first day I met her, she's been strong, fierce, and independent. I can't really imagine a time when she would need us to protect her, but if anyone ever hurt her...Alec, I'd kill them. I love her to death, I would never want to see her hurt in any way. So if this idiot screws it up, we'll have a 'meeting' with him not too long afterwards."

Alec nodded. "There are times when Izzy needs someone to take care of her, she's just too proud to admit it. Granted, so are we, but still." His gaze lingered back to his sister once more; she really had grown up into a strong, intelligent, beautiful young woman, and a part of his heart would always belong to her. For so long, Alec and Jace were her boys, the only two men besides their father that she trusted without a doubt. But now Simon was a part of that, and it bothered Alec; sure, he was happy for them, but he didn't like the thought of Simon's grubby little vampire hands anywhere near his sister. He knew that he was always going to be her big brother, but it was hard to acknowledge that there was a new man in her life now that actually meant something, one that wasn't just a fling.

Jace's voice broke through his thoughts. "It does make me feel a little better to know that she can handle herself just fine. But we'll always be there for backup."

Alec smiled and nodded. "Yeah we will."

* * *

 **AN:** So, how was it? I'm sorry that there was so much Simon bashing; I actually love Sizzy, but I did what I had to do. I hope you guys liked it, and thank you so much for reading, reviewing, favoriting, and following, if you do! Later!


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